Controlling operation of exhaust of an engine including a particulate filter

ABSTRACT

Methods and systems for controlling operation of exhaust of an engine including a particulate filter are described. One example method includes generating compressed air during engine operation, and storing the compressed air. The method further includes, during or after engine shutdown, pushing the compressed air through the particulate filter using a pressure of the compressed air.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/648,839 filed on Dec. 29, 2009, now U.S. Pat. No. 8,347,613, whichclaims priority to U.S. Provisional Patent Application Ser. No.61/246,944, entitled “PARTICULATE FILTER REGENERATION DURING ENGINESHUTDOWN,” filed Sep. 29, 2009, the disclosure of each of which arehereby incorporated by reference in its entirety and for all purposes.

TECHNICAL FIELD

The present application relates generally to an engine having an exhaustsystem which includes a particulate filter.

BACKGROUND AND SUMMARY

Direct injection (DI) engines may produce more soot than port fuelinjected engines in part due to diffuse flame propagation. As aconsequence of diffuse flame propagation, fuel may not adequately mixwith air prior to combustion, resulting in pockets of rich combustionthat generate soot. Further, DI engines may be susceptible to generatingsoot during high load and/or high speed conditions when there is a lackof sufficient air and fuel mixing.

The inventors herein have recognized various issues in applyingparticulate filters to DI, spark-ignition engines. For example, it canbe difficult to maintain accurate emission control during particulatefilter regeneration in a DI, spark-ignition engine.

Thus, methods and systems for controlling operation of exhaust of anengine including a particulate filter are described. One example methodincludes generating compressed air during engine operation and storingthe compressed air. Thus, the method may include, during or after engineshutdown, pushing the compressed air through the particulate filterusing a pressure of the compressed air.

By performing a particulate filter regeneration during and/or afterengine shutdown, the particulate filter can be regenerated by anincreased flow of oxygen to the particulate filter while avoidingpotential increased emissions from a three-way catalyst in an exhausttailpipe.

In one example, the method may include pushing compressed air throughthe particulate filter in a direction that is the same direction asexhaust flow during engine combustion. In this way, it may be possiblemaintain more commonality in control between engine running and engineshutdown regenerations.

Also, if an engine running regeneration (e.g., during engine combustion)is carried out when engine shutdown is requested, the particulate filterregeneration can be continued through engine shutdown conditions withoutchanges in a direction of airflow at the particulate filter.

Yet another potential advantage of regenerating the filter during and/orafter engine shutdown using stored compressed air is that a regenerationreaction can be delayed or advanced to a time when particulate filterconditions are appropriate for carrying out the regeneration reaction.For example, compressed air may be stored until the particulate filtertemperature becomes hot enough to carry out the regeneration reaction.Further still, particulate filter regeneration may be selectivelycarried out under particular engine shutdown conditions (e.g., shutdownsin which filter regeneration is already commenced during engine runningconditions, or shutdowns in which filter temperature is high enough),and not during others.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine with a turbocharger and anexhaust gas recirculation system.

FIG. 2 shows a flowchart illustrating a method for managing particulatefilter regeneration in a direct injection gasoline engine in a vehicle.

FIG. 3 shows a flowchart illustrating a method for storing compressedair during engine shutdown.

FIG. 4 shows a flowchart illustrating a method for regenerating aparticulate filter during engine shutdown, using stored compressed air.

FIG. 5 shows a flowchart illustrating a method for starting an enginebased on filter regeneration carried out during and/or after a previousengine shutdown.

DETAILED DESCRIPTION

The following description relates to a method for regenerating aparticulate filter in an engine, such as a direct injection gasolineengine. During a first operating condition of the engine, combustion inthe engine may be carried out about stoichiometry and exhaust gas mayflow from the engine in a first direction, to a particulate filter wheresoot generated by the engine is collected. During engine operationcompressed air generated by turbocharger motion (or vacuum generated byengine spinning), may be stored in the intake system, such as in theintake manifold. Then during a subsequent engine shutdown (e.g., duringengine spin- down after combustion has stopped, or during engine rest),the stored vacuum or pressure may be applied to generate regenerationflow to the filter. For example, pressure created by stored compressedair in an intake manifold may be used to push air from the intakemanifold to the particulate filter in a first direction consistent witha direction of exhaust airflow during engine combustion, to aid infilter regeneration. Alternatively, stored vacuum may be used to drawfresh air into the filter from ambient atmosphere (e.g., via thetailpipe and/or engine inlet) in a second, reverse direction, to aid infilter regeneration.

In some embodiments, one or more exhaust gas recirculation (EGR) systemsmay be utilized to allow the air to flow from the intake manifold to thefilter via the stored compressed air. For example, when compressed airis stored in an intake manifold, a particulate filter can be regeneratedby causing air to flow from the intake manifold, through a high pressureEGR system, and then through a particulate filter in a first directionfrom an exhaust side of the particulate filter to an atmospheric side ofthe particulate filter. In another example, air may flow from the intakemanifold, through a low pressure EGR system and through the particulatefilter in a second, reverse direction. Still other variations may beused.

Turning now to FIG. 1, a schematic diagram shows one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof an automobile. Engine 10 may be controlled at least partially by acontrol system including controller 12 and by input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Combustion chamber(i.e., cylinder) 30 of engine 10 may include combustion chamber walls 32with piston 36 positioned therein. In some embodiments, the face ofpiston 36 inside cylinder 30 may have a bowl. Piston 36 may be coupledto crankshaft 40 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 40 maybe coupled to at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

Intake valve 52 may be controlled by controller 12 via electric valveactuator (EVA) 51. Similarly, exhaust valve 54 may be controlled bycontroller 12 via EVA 53. Alternatively, the variable valve actuator maybe electro hydraulic or any other conceivable mechanism to enable valveactuation. During some conditions, controller 12 may vary the signalsprovided to actuators 51 and 53 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve52 and exhaust valve 54 may be determined by valve position sensors 55and 57, respectively. In alternative embodiments, one or more of theintake and exhaust valves may be actuated by one or more cams, and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Intake passage 42 may include throttles 62 and 63 having throttle plates64 and 65, respectively. In this particular example, the positions ofthrottle plates 64 and 65 may be varied by controller 12 via signalsprovided to an electric motor or actuator included with throttles 62 and63, a configuration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, throttles 62 and 63 may be operated tovary the intake air provided to combustion chamber 30 among other enginecylinders, and may also be operated to control a pressure of compressedair, or a vacuum in the intake manifold, as will be discussed. Thepositions of throttle plates 64 and 65 may be provided to controller 12by throttle position signals TP. Intake passage 42 may include a massair flow sensor 120 and a manifold air pressure sensor 122 for providingrespective signals MAF and MAP to controller 12.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164 (e.g., via a shaft)arranged along exhaust passage 48. For a supercharger, compressor 162may be at least partially driven by the engine and/or an electricmachine, and may not include a turbine. Thus, the amount of compressionprovided to one or more cylinders of the engine via a turbocharger orsupercharger may be varied by controller 12. Further, turbine 164 mayinclude wastegate 166 to regulate the boost pressure of theturbocharger. Similarly, intake manifold 44 may include valved bypass167 to route air around compressor 162.

As shown, throttle 62 is positioned downstream of compressor 162 anddownstream of the valved bypass 167 and throttle 63 is positionedupstream of both the compressor 162 and the valved bypass 167. Selectivecontrol of these throttles, as positioned, may allow for greater controlof generation and storage of compressed air or vacuum in a portion ofthe intake manifold. As will be discussed, the generation of compressedair or vacuum in said portion of the intake manifold can be used forregeneration of the particulate filter.

In the disclosed embodiments, and as illustrated in FIG. 1, an exhaustgas recirculation (EGR) system may route a desired portion of exhaustgas from exhaust passage 48 to intake manifold 44 via high pressure EGR(HP-EGR) passage 140 or low pressure EGR (LP-EGR) passage 150.

An HP-EGR passage 140 may have a first opening upstream of the turbineand particulate filter, such that exhaust gas can be routed fromupstream of the turbine 164 of the turbocharger to a second openingdownstream of the compressor 162 of the turbocharger and the throttle 62during engine combustion. The LP-EGR passage 150 may have a firstopening downstream of the turbine 164 and downstream of device 72 (e.g.,particulate filter) such that exhaust gas can be routed from downstreamof the device 72 to a second opening upstream of the compressor 162 yetdownstream of throttle 63, during engine combustion. In someembodiments, engine 10 may include only an HP-EGR system or only anLP-EGR system.

An amount of EGR flow may be varied by selective control of HP-EGR valve142 or LP-EGR valve 152 during engine combustion operation. Further, anEGR sensor, such as HP-EGR sensor 144, may be arranged within either orboth of the HP-EGR and LP-EGR passages and may provide an indication ofone or more of pressure, temperature, and concentration of the exhaustgas therein. Alternatively, the HP-EGR valve and/or LP-EGR valve may becontrolled through a calculated value based on signals from the MAFsensor (upstream of throttle 63), MAP (intake manifold), MAT (manifoldgas temperature) and the crank speed sensor. Further still, flow througheither or both of the HP-EGR and LP-EGR passages may be controlled basedon an exhaust O₂ sensor and/or an intake oxygen sensor (e.g., in anintake manifold). Under some conditions, an EGR system may be used toregulate the temperature of the air and fuel mixture within thecombustion chamber.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control system 70. Further, sensor 127 is shown coupled toexhaust passage 48 upstream of emission control device 72 (e.g., aparticulate filter) and sensor 128 is shown coupled to exhaust passage48 downstream of emission control device 72. Sensors 126, 127, and 128may be a combination of any suitable sensors for providing an indicationof exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO(universal or wide-range exhaust gas oxygen), a two-state oxygen sensoror EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor.

Emission control device 71 and 72 are shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 71 and device 72may include a selective catalytic reduction (SCR) system, three waycatalyst (TWC), NO_(x) trap, various other emission control devices, orcombinations thereof. For example, device 71 may be a TWC and device 72may be a particulate filter (PF). In some embodiments, where device 72is a particulate filter, device 72 may be located downstream of device71 (as shown in FIG. 1). In other embodiments, device 72 may be aparticulate filter positioned upstream of device 71, which may be a TWC(this configuration not shown in FIG. 1). Further, in some embodiments,during operation of engine 10, emission control devices 71 and 72 may beperiodically reset by operating at least one cylinder of the enginewithin a particular air/fuel ratio. In still further embodiments, device72 (e.g., particulate filter) may be regenerated while the engine isshut down (e.g., not combusting), as will be described in detail below.Additionally, a tailpipe valve 199 is shown downstream of device 72 inexhaust tailpipe 198. The tailpipe valve 199 may be controlled bycontroller 12, in order to control pressure in the exhaust. This will bediscussed in detail below.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor 102, input/output ports 104, an electronic storage mediumfor executable programs and calibration values shown as read only memory106 in this particular example, random access memory 108, keep alivememory 110, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Note that various combinations of the above sensors maybe used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft.

Storage medium read only memory 106 can be programmed with computerreadable data representing instructions executable by microprocessor 102for performing the methods described below as well as other variantsthat are anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Example control routines for an engine, such as engine 10 describedabove with reference to FIG. 1 are shown and described with respect toFIGS. 2-5. FIG. 2 is a flowchart illustrating a method for managingparticulate filter regeneration in a direct injection gasoline. FIG. 3illustrates example engine shutdown control for storing compressed air.FIG. 4 is a flowchart illustrating control of an engine shutdown, orengine rest, regeneration using stored compressed air, and FIG. 5 is aflowchart illustrating an example routine for starting an engine thattakes into account whether, and to what extent and/or duration, engineshutdown filter regeneration was carried out before said starting of theengine.

Turning now to FIG. 2, an operational flow chart illustrating a method200 for managing regeneration of a particulate filter downstream of anengine, such as engine 10 shown in FIG. 1, is shown. Specifically,method 200 demonstrates example operation for managing particulatefilter regeneration of a direct injection gasoline engine, based onengine operating conditions. The method 200 may include determiningwhether engine shutdown regeneration is requested, and determining atiming for an engine shutdown regeneration.

At 210 of method 200, the method includes determining whether the engineis running This may include determining whether the engine is spinningand carrying out combustion of one or more cylinders. In one example,combustion may include oscillation of the engine air-fuel ratio aboutstoichiometry, where exhaust gas flows from the engine, through aturbine (e.g., turbine 164), and then through a three-way catalyst(e.g., device 71) and a particulate filter (e.g., device 72) beforeexiting through a tailpipe (e.g., exhaust tailpipe 198). If the engineis not running, the method 200 may end. If the engine is currentlyrunning, the method 200 may proceed to 212.

At 212, an amount of particulate (e.g., soot) in the particulate filteris estimated. In some embodiments, this may include estimating an amountof soot in the particulate filter based on a pressure drop across theparticulate filter. In other embodiments, a soot accumulation model maybe utilized to estimate the amount of soot in the particulate filter.Once the amount of soot is determined, the method continues to 214 todetermine if the amount of soot is greater than a threshold amount(e.g., a first, lower threshold A) which may be used as an indication ofwhether or not to regenerate the particulate filter during and/or afteran engine shutdown.

If the estimated amount of soot is less than the threshold A, the method200 may continue to 228 where a non-regeneration engine shutdown isrequested (e.g., where, if the engine is shut down, the particulatefilter is not regenerated during engine shutdown and/or during enginerest). For example, the method 200 may include setting a flag indicatingthat a request for non-regeneration engine shutdown has beenestablished. On the other hand, if the estimated amount of soot exceedsthe threshold A, the method 200 may proceed to 216 to request an engineshutdown regeneration (see FIG. 3). Then, the method 200 may continue to218 to determine if the amount of particulate stored in the particulatefilter is greater than a threshold amount (e.g., a second, higherthreshold B), which may be used as an indication of whether or not toregenerate the particulate filter during engine running, or enginecombustion (e.g., before an engine shutdown). If the answer to 218 isyes, the method 200 may continue to 220 to request an engine runningregeneration at 220. Otherwise, the method 200 may end.

At 222, the method 200 includes determining whether regenerationconditions have been met. For example, it may be determined whetherexhaust temperature is greater than a threshold (e.g., a minimumregeneration temperature), or other conditions. In this way, aregeneration reaction can be delayed or advanced to a time whenparticulate filter conditions are appropriate for carrying out theregeneration reaction. For example, the stored pressure may be storeduntil the particulate filter temperature becomes hot enough to carry outthe regeneration reaction.

At 224, the routine performs the engine running particulate filterregeneration. In some examples, an engine running particulate filterregeneration may include adjusting engine operation to raise exhaust gastemperature sufficiently high to initiate filter regeneration withexcess oxygen. For example, engine speed can be increased to increaseexhaust gas temperature. For example, engine speed can be increased toincrease exhaust gas temperature. During engine running regeneration,the excess oxygen for particulate filter regeneration may be suppliedvia one or more of the EGR systems (e.g., by delivering pressurized airfrom the intake to the exhaust, thus bypassing the engine), via an airpump delivering airflow upstream of the particulate filter anddownstream of the three way catalyst (e.g., delivery of ram-air), byoperating with lean combustion in the engine, or combinations thereof.In one example, during the engine running regeneration of 224, excessoxygen flows to and through the particulate filter in a direction fromthe exhaust manifold side, or engine output side of the filter to thetailpipe, or atmospheric side of the filter. Various operatingparameters may be adjusted to control the filter regeneration rate,temperature of the exhaust and/or particulate filter, etc.

Referring now to FIG. 3, a method 300 illustrating additional details ofengine shutdown control is described. First, at 310, the method 300includes determining whether an engine shutdown request has been made.For example, the engine shutdown request may be generated from anoperator indicating a request to shut down the vehicle (e.g., by aturn-off the vehicle via a key position of the vehicle). The engineshutdown request may also be generated based on vehicle operatingconditions where engine output torque is not needed, for example, duringdeceleration conditions where the requested engine torque is less thanzero, or in response to a driver tip-out. In still another example, theengine shutdown request may be generated from a hybrid-vehiclecontroller if an engine is in a hybrid electric vehicle, where an engineshutdown can be carried out while the vehicle continues to operateand/or travel, driven by a hybrid propulsion system.

When the answer to 310 is yes, the method continues to 312 to determinewhether engine shutdown regeneration was requested (e.g., at 220 ofmethod 200). If so, the method 300 continues to 316. Otherwise, themethod 300 may continue to 314 to determine if an engine runningregeneration is already in progress at the time of the engine shutdownrequest. In this case, even though an engine shutdown regeneration wasnot specifically requested, in some conditions, it may be beneficial toextend the engine running regeneration through engine shutdown. That is,engine shutdown regeneration may be selectively performed by the methodsprovided herein. Specifically, the regeneration may be extended fromengine running operation, through engine spin-down, and through at leasta portion of engine rest. Thus, if the answer to 314 is yes, the method300 may also continue to 316, at least under selected conditions (e.g.,when there is a sufficient amount of particulate stored in the filter,greater than a minimum amount C) to warrant extending regenerationthrough the engine shutdown. In this example, the operations indicatedat 316-322 of the method 300 may be carried out while particulate filterregeneration is already underway. Otherwise, the method 300 may end.

If the answer to 314 is no, the method 300 may carry out anon-regeneration engine shutdown (not shown). For a non-regenerationengine shutdown, the method 300 may include reducing, or avoiding astoring of increased pressure and/or vacuum during the engine shutdown,and thus does not increasing excess oxygen to the particulate filterduring engine shutdown operation to regenerate, or extend regenerationof, the particulate filter. Accordingly, particulate filter regenerationmay be selectively carried out under particular engine shutdownconditions (e.g., engine shutdowns in which filter regeneration isalready commenced during engine running conditions) in some cases, andnot during others.

At 316, the method 300 includes compressing air in the intake manifold,and storing the compressed air. In order to generate compressed air(e.g., compressed with respect to atmospheric pressure) in the intakemanifold, engine boost may be increased (via adjustment of a turbinewastegate or a valved bypass of a compressor, for example), and athrottle opening may also be increased during a portion of engineshutdown. In some examples, generation of compressed air includesdrawing an amount of air into the intake manifold that exceeds the useof air by the engine. The increasing of engine boost and/or throttleopening may be initiated during engine spin-down. By increasing athrottle opening, the amount of air being drawn into intake manifold canbe increased. In another example, the HP-EGR valve and/or LP-EGR valvemay also be closed during engine spin-down, in order to createcompressed air and/or increase an amount of pressure in the intakemanifold. In some cases, the tailpipe valve may be closed during aportion of engine shutdown to increase intake manifold pressure.

Alternately, at 316, the method may include adjusting operation togenerate and/or store vacuum. The stored vacuum may be generated in theintake manifold by reducing engine boost and throttle opening before theengine stops spinning In this way, vacuum in the intake manifold, can begenerated and stored.

Additional adjustments to further increase stored compressed air orstored vacuum (e.g., in the intake manifold) may be carried out, such asadjusting valve timing. Such adjustments may be concurrent withdiscontinuing combustion in one or more (e.g., all) of the enginecylinders. In this way, it is possible to either increase pressure orgenerate vacuum in the intake manifold via the rotating engine duringengine spin-down, even if the engine speed is decelerating. Compressedair and/or a vacuum may be generated and stored either before, or afterdiscontinuation of combustion, and either before or during enginespin-down. Further, while this example illustrates storing pressureand/or vacuum in the intake manifold, pressure and/or vacuum may bestored at other locations in the intake, such as a pressure or vacuumstorage tank coupled to the intake manifold. Further, pressure and/orvacuum can be stored at any location in the air circulation circuits ofan engine, provided there are appropriate valves and controls forcontrolling the generation, storage, and movement of the stored pressureor vacuum.

Next, at 318, the method includes maintaining the pressure of thecompressed air (or vacuum) in the intake manifold while shutting downthe engine, for example, by maintaining the throttle in a sealed closedposition in the intake passage. To maintain compressed air in the intakemanifold, the throttle may be closed at a maximum air charge, or when amaximum air charge exists in the portion of the intake manifold thatstores the generated compressed air.

In the case where vacuum has been generated, vacuum may be maintained inthe intake manifold by moving the throttle from almost closed to fullyclosed as the engine spins down to rest, such that the throttle is fullyclosed as engine speed drops below a minimum engine speed, such as 50RPM. By sealing the throttle closed and by stopping the engine at aposition such that there is little or no communication between theintake manifold and exhaust manifold through one or more cylinders ofthe engine (e.g., without positive valve overlap of any one cylinder inthe rest position), it may be possible to temporarily store thegenerated vacuum (or compressed intake gasses) even after the enginecomes to rest. The LP-EGR and/or HP-EGR valves may also be sealed closedin order to assist in the storage of the generated vacuum, or compressedair.

During the engine shutdown, the method 300 may include adjustingoperating parameters to increase exhaust temperature at 320. Forexample, if a particulate filter temperature is less than a thresholdtemperature, increasing exhaust temperature may include operating theengine with a retarded spark timing to increase exhaust temperature inpreparation for shutdown regeneration. This may be carried out for aselected number of combustions, including one or more last combustionevents before discontinuing combustion.

At 322, the method 300 includes carrying out the engine shutdownregeneration. For example, the method 300 may include temporarilystoring the compressed air or generated vacuum in the intake until apeak particulate filter temperature, or temperature range, is reached,and thereafter dissipating the compressed air or stored vacuum at 322.Because temperatures may temporarily rise after a shutdown operation,the method 300 may include maintaining the compressed air or the vacuumuntil the peak filter temperature, or temperature range, is reachedbefore adjusting one or more valves to use the vacuum or compressed airto increase oxygen flow to the particulate filter, and thus regeneratethe particulate filter. In this way, fresh air will be drawn in to aparticulate filter when the particulate filter is subject to a favorabletemperature for carrying out the regeneration reaction. In anotherexample, the method 300 may include increasing the flow of air at theparticulate filter as the exhaust temperature temporarily increasesduring an engine shutdown.

Additional details of engine shutdown regeneration are described withregard to FIG. 4, for example. Specifically, the method 400 includesdetermining, at 410, whether temperature is greater than a thresholdtemperature value. For example, the method 400 may include determiningif temperature has risen during engine shutdown and/or engine restconditions to above the threshold temperature, or if it was alreadyabove a threshold temperature before the engine shutdown. In this way,it can be further determined whether or not to perform engine shutdownregeneration. The fresh air to the particulate filter may be pushedthrough via pressure of compressed air (or may be drawn in via storedvacuum) at different times after the engine has stopped, based ondifferent temperature conditions of the exhaust, for example. Additionalparameters may also be monitored at 410, including whether the enginehas come to a complete stop, and/or whether stored compressed air isgreater than a threshold level (e.g., whether pressure in the intakemanifold is great enough to be able to push a desired amount of oxygento the particulate filter).

When the answer to 410 is yes, the method 400 continues to 412 to adjustone or more EGR system parameters and/or intake or exhaust systemparameters to push air through the particulate filter via the compressedair in the intake. In other examples, air may be drawn toward theparticulate filter via stored vacuum in the intake. The adjusting of theflow through the filter may be based on feedback of various sensors, asdescribed herein.

In an example where compressed air has been stored in the intakemanifold, the LP-EGR system may be closed during filter regeneration oromitted, and a tailpipe valve may be left open during filterregeneration or omitted. Thus, upon opening of the turbine wastegateand/or HP-EGR valve, the fresh air flows from the intake manifold,through the HP-EGR passage to the exhaust, past the turbine (e.g.,through an at least partially opened wastegate, or through the turbine),and then through the particulate filter and to the atmosphere. Here, oneor more of the HP-EGR valve, wastegate valve, or tailpipe valve may beadjusted to control the timing and amount of fresh air flowing past theparticulate filter. Note in this example, the airflow during an engineshutdown filter regeneration travels in the same direction as exhaustflow during engine combustion.

For example, compressed air may be released by opening a tailpipe valveand a LP-EGR valve and closing a HP-EGR valve, thereby pushing thecompressed air from the intake manifold through the LP-EGR passage, andthrough the particulate filter from an atmospheric side of theparticulate filter to an engine output side of the particulate filter,thereby bypassing the three-way catalyst.

In another example where compressed air has been stored in the intakemanifold, an HP-EGR system may be closed or omitted. The LP-EGR valveand compressor valved bypass may be opened during particulate filterregeneration, the throttle upstream of a compressor may be closed, andthe tailpipe valve may be closed. As such, upon opening of thecompressor valved bypass, the compressed air may flow from the intakemanifold, through the LP-EGR system, through the particulate filter froman atmospheric side to an engine output side of the particulate filter(e.g., in a reverse direction, compared to the direction of exhaust flowduring engine combustion). The turbine wastegate valve may also beopened during particulate filter regeneration, to allow the compressedair to bypass the turbine.

In some cases, the compressed air may be pushed through the particulatefilter in the reverse direction opposite the direction of exhaust flowduring engine combustion until pressure in the intake manifold andexhaust passage are equalized. Thereafter, the HP-EGR valve may beopened and the LP-EGR valve may be closed and air may be pushed throughthe particulate filter from the engine output side of the particulatefilter to the atmospheric side of the particulate filter.

In an example where a vacuum has been generated in the intake manifold,both the HP-EGR and LP-EGR passages may be used during the particulatefilter regeneration, where a compressor bypass is closed (e.g., valvedbypass 167 of FIG. 1 is closed), a turbine wastegate is at leastpartially opened, and the tailpipe valve is closed. In this case, boththe HP-EGR valve and LP-EGR valve (e.g., HP-EGR valve 142 and LP-EGRvalve 152 of FIG. 1) are each at least partially opened to initiate theflow of fresh air to the particulate filter. Thus, if a vacuum has beengenerated in the intake manifold, fresh air can be drawn in from intakepassage (e.g., by opening a throttle), pass through the LP-EGR passage,and flow through the particulate filter in a reverse direction. That is,the airflow may travel through the particulate filter in a directionopposite to an exhaust gas flow direction when the engine is runningFrom the particulate filter, the fresh airflow travels around theturbine via the turbine wastegate and then through the HP-EGR passage tothe intake manifold.

In another example in which a vacuum has been generated in the intakemanifold, fresh air may be drawn in through the particulate filter byopening a tailpipe valve downstream of the particulate filter (ifequipped), the turbine wastegate valve, and/or the HP-EGR valve. In thiscase, the LP-EGR valve may be closed or the LP-EGR passage may beomitted. The fresh airflow may be drawn in through the tailpipe, passthrough the particulate filter in a reverse direction compared to thedirection of exhaust during engine combustion operation (e.g., from anatmospheric side of the particulate filter to an engine output side ofthe particulate filter), past the turbine (e.g., though an at leastpartially opened wastegate valve, or through the turbine), and then passthrough the HP-EGR passage to enter the intake manifold. This mayeffectively dissipate the stored vacuum. In this case, the method mayinclude adjusting the amount of fresh airflow through the filter duringengine shutdown conditions and/or the timing of fresh air flow bybyadjusting the opening of one or more of an HP-EGR valve, an LP-EGRvalve, and a tailpipe valve.

Combinations of the methods provided herein for flowing excess oxygenthrough the particulate filter may be employed. For example, a firstmethod for flowing compressed air through the particulate filter in areverse direction may be carried out until pressure in the intakemanifold has equalized with pressure in the exhaust passage. Thereafter,a second method for flowing compressed air through the particulatefilter in a first direction (e.g., same direction as exhaust flow duringengine combustion) may be carried out.

The timing and/or amount of fresh airflow flowing past a particulatefilter may be regulated by adjusting one or more of a throttle opening,a turbine wastegate, a compressor valved bypass, a tailpipe valve, anHP-EGR valve, and an LP-EGR valve. For example, under higher temperatureshutdown conditions, the stored compressed air or vacuum may be used ata first, earlier timing following a discontinuation of enginecombustion, to take advantage of a high particulate filter temperature.However, under lower temperature conditions, the stored compressed airor vacuum may be used at a second, later timing following thediscontinuation of engine combustion, to enable the airflow to passthrough the filter in coordination with a natural temperature rise atthe particulate filter.

The timing and/or amount of fresh airflow may also be regulated based onan amount of excess oxygen detected at the particulate filter by anoxygen sensor. In the case where compressed air or excess oxygen isbeing pushed through the particulate filter in a direction that is thesame as a direction of exhaust flow during engine combustion (e.g., fromtailpipe to atmosphere), a first oxygen sensor upstream of theparticulate filter may provide an excess oxygen measurement upon whichairflow adjustments can be made. Further, this approach may also be usedduring engine running filter regeneration to control an amount of excessoxygen delivered to the filter. Alternatively, in the case where air ispushed through the particulate filter in a reverse direction, or where avacuum draws in air through the particulate filter in the reversedirection, a second oxygen sensor downstream of the particulate filtermay provide an excess oxygen measurement upon which airflow adjustmentsare made.

In some cases, it may be possible to adjust engine operation while anengine is still combusting so that during a subsequent engine shutdown,it is possible to generate excess oxygen flow past the filter to performparticulate filter regeneration. For example, valve positioning and/orengine combustion parameters may be adjusted during one or more lastcombustions before discontinuing combustion. Furthermore, an engineshutdown regeneration may include a continuation or extension of enginerunning regeneration, or it may solely be engine shutdown regeneration(e.g., initiated during engine shutdown), at least under someconditions. Such an engine shutdown may be contrasted with an engineshutdown not having particulate filter regeneration.

Finally, the flow chart in FIG. 5 illustrates a control routine 500 forstarting an engine after engine shutdown regeneration of the particulatefilter, without any other starts between the shutdown regeneration andthe current start. Specifically, routine 500 adjusts engine operatingparameters during engine start based on a state and extent of theregeneration during and/or after engine shutdown.

At 510 of routine 500 it is determined if the vehicle is on by checkingif a key is on, in this example. In some embodiments, such as when thevehicle has a hybrid-electric propulsion system, the key may haveremained on during engine shutdown, and thus other parameters (e.g.,battery state of charge, desired engine speed, engine load, etc.) may bechecked at 510 to determine if an engine restart is desired. If it isdetermined that the key is not on, routine 500 may end.

On the other hand, if it is determined that the key is on at 510,routine 500 proceeds to 512 where it is determined if regeneration wasattempted or at least partially carried out during a previous engineshutdown. In some embodiments, an engine shutdown may be performedwithout regeneration of the particulate filter (e.g., without drawing inor pushing air via stored vacuum or stored compressed air,respectively). If it is determined that regeneration was not attemptedor successfully completed during a previous engine shutdown, routine 500may proceed to 522 where the engine is started without adjustments for aprevious filter regeneration. This may include starting the engine witha first air-fuel ratio profile, idle speed set-point, spark timingprofile, etc. In one example, an air-fuel ratio of an initial combustionevent of the start may be adjusted to be less lean or more rich, inresponse to a less extensive (or lack of) engine shutdown filterregeneration.

However, if it is determined that an engine shutdown regeneration wasattempted and/or successfully completed during a previous engineshutdown, routine 500 may continue to 514 where the state ofregeneration is determined. For example, regeneration may have beenstarted, but then discontinued due to an engine start request. Asanother example, regeneration may have started and been terminatedbefore the regeneration of the particulate filter was completed (e.g.,regeneration was partially completed). In further examples, regenerationmay have been started but only a portion of stored soot may have beenremoved by regeneration. Further still, depending on a temperature ofthe three-way catalyst during a previous engine shutdown regeneration,more or less excess oxygen may have been stored at the three-waycatalyst. As such, a state of a three-way catalyst may also bedetermined at 514.

Once the state of regeneration is determined, routine 500 of FIG. 5proceeds to 518 where the engine is started. Then routine 500 continuesto 520 where engine operating parameters are adjusted based on the stateof regeneration. Engine operating parameters may include, but are notlimited to, air fuel ratio, spark timing, idle speed setpoint, etc. Forexample, if the regeneration was attempted and only partially completed,there may be less 0 ₂ in the three way catalyst than if the regenerationhad been more fully carried out. As such, the air fuel ratio may beadjusted during the engine start to be more rich (or less lean) ofstoichiometry in order to reduce the excess O₂ in the three-way catalystduring the engine start. In some cases, engine operating parameters maybe adjusted based on the state of the three-way catalyst.

In another example, the engine may be started in such a way as tocontinue regeneration if it was not completed during engine shutdown,and/or if an engine shutdown regeneration is ongoing. For example, in avehicle with a hybrid-electric propulsion system that carried out anengine shutdown regeneration while the engine was still spinning (e.g.,driven by a motor), the engine may need to be restarted as the vehicleaccelerates, and as such, the engine shutdown regeneration of theparticulate filter may not have completed. Thus, the air fuel ratio maybe adjusted to be lean of stoichiometry and the spark timing may beretarded in order to continue to supply the particulate filter withexcess O₂ for regeneration. Therefore, based on the state of theregeneration during engine shutdown, the engine may be started in amanner so as to continue the regeneration or reduce the effects of theregeneration on components such as the three way catalyst.

As described above with reference to the figures, a direct-injectiongasoline engine may have a particulate filter coupled to its exhaustsystem to collect soot generated during operating conditions, such aswhen the engine is subject to high speed and/or high load. Further, inorder to maintain engine efficiency, the particulate filter may beregenerated, at least partially and at least under some conditions,while the engine is shut down. Based on operating conditions and thevehicle system, stored vacuum and/or pressure in the intake may be usedto facilitate regeneration of the particulate filter during engineshutdown.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The invention claimed is:
 1. A method for controlling operation ofexhaust of an engine including a particulate filter, comprising:generating compressed air during stoichiometric engine operation via aturbocharger and storing the compressed air; and maintaining thecompressed air stored until a threshold temperature is reached afterengine shutdown, and then pushing the compressed air through theparticulate filter using a pressure of the compressed air.
 2. The methodof claim 1, wherein storing the compressed air includes storing thecompressed air in an intake manifold of the engine.
 3. The method ofclaim 2, further comprising, after engine shutdown, opening an HP-EGRvalve, and wherein pushing the compressed air includes pushing thecompressed air from the intake manifold through an HP-EGR system to theparticulate filter to regenerate the particulate filter.
 4. The methodof claim 1, further comprising, after engine shutdown, adjusting anamount of the compressed air pushed through the particulate filter basedon an exhaust gas sensor located between the engine and the particulatefilter.
 5. The method of claim 1, further comprising regenerating theparticulate filter after engine shutdown conditions during engine restby flowing air through the particulate filter from an engine output sideof the particulate filter to an atmospheric side of the particulatefilter.
 6. The method of claim 5, further comprising continuingregeneration of the particulate filter after engine shutdown using thepressure of the compressed air.
 7. The method of claim 2, furthercomprising, after engine shutdown, opening an LP-EGR valve and closingan HP-EGR valve, and where pushing the compressed air includes pushingthe compressed air from the intake manifold, through an LP-EGR system,and through the particulate filter from an atmospheric side of theparticulate filter to an engine output side of the particulate filter.8. The method of claim 1, further comprising adjusting an engineoperating parameter during an engine start subsequent to the engineshutdown, based on a particulate filter regeneration during or after theengine shutdown.
 9. The method of claim 8, wherein the engine operatingparameter is an air-fuel ratio of an initial combustion of the enginestart.
 10. A method for controlling engine system with a cylinder, anintake manifold, and a particulate filter, comprising: compressing airin the intake manifold during engine operation via a turbochargercompressor with an intake throttle opening increased; storing thecompressed air in the intake manifold by sealing the intake throttleclosed; and during or after an engine shutdown, pushing the compressedair through the particulate filter via a pressure of the compressed airto regenerate the filter.
 11. The method of claim 10, wherein the enginesystem further comprises one or more valves, the method furthercomprising adjusting an amount of air pushed through the particulatefilter by adjusting the one or more valves.
 12. The method of claim 11,wherein the engine system further comprises an HP-EGR system, the methodfurther comprising adjusting the one or more valves to push thecompressed air through the HP-EGR system to the particulate filter toregenerate the particulate filter.
 13. The method of claim 11, whereinthe engine system further comprises an LP-EGR system, the method furthercomprising adjusting the one or more valves to push the compressed airfrom the intake manifold through an LP-EGR passage, and through theparticulate filter to an exhaust passage to regenerate the particulatefilter.
 14. The method of claim 11, wherein the one or more valvesincludes one or more of a throttle, a tailpipe valve, a compressorbypass valve, a turbine wastegate valve, an HP-EGR valve, and an LP-EGRvalve.
 15. The method of claim 11, further comprising initiatingregeneration of the particulate filter during engine running conditionsby flowing air through the particulate filter, and continuing theregeneration during or after engine shutdown by pushing the compressedair through the particulate filter via the pressure of the compressedair.
 16. A method for controlling operation of an engine exhaustincluding a particulate filter, comprising: generating compressed airduring boosted engine operation by increasing intake throttle opening;storing the compressed air in an intake manifold during engine shutdownby sealing the intake throttle closed; maintaining the compressed airstored while shutting down an engine; and after engine shutdown and uponreaching a threshold filter temperature, pushing the compressed airthrough the particulate filter.
 17. The method of claim 16 furthercomprising, during the pushing, closing an intake throttle upstream of aturbocharger compressor, wherein during engine operation exhaust flowsthrough the particulate filter in a forward direction, and whereinpushing the compressed air includes opening a compressor bypass valve,opening an LP-EGR valve, closing an exhaust throttle valve downstream ofthe particulate filter, and pushing the compressed air in a reverse flowthrough the particulate filter.
 18. The method of claim 16, whereinpushing the compressed air includes opening a turbocharger wastegatevalve, and opening an HP-EGR valve.